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SubjectRe: [PATCH 6/6 v3] blkio-cgroup: Document for blkio.use_hierarchy interface
Vivek Goyal wrote:
> On Mon, Dec 27, 2010 at 04:51:20PM +0800, Gui Jianfeng wrote:
>> Document for blkio.use_hierarchy interface
>>
>> Signed-off-by: Gui Jianfeng <guijianfeng@cn.fujitsu.com>
>> ---
>> Documentation/cgroups/blkio-controller.txt | 70 ++++++++++++++++++++--------
>> 1 files changed, 51 insertions(+), 19 deletions(-)
>>
>> diff --git a/Documentation/cgroups/blkio-controller.txt b/Documentation/cgroups/blkio-controller.txt
>> index 4ed7b5c..bd01d6c 100644
>> --- a/Documentation/cgroups/blkio-controller.txt
>> +++ b/Documentation/cgroups/blkio-controller.txt
>> @@ -91,30 +91,51 @@ Throttling/Upper Limit policy
>>
>> Hierarchical Cgroups
>> ====================
>> -- Currently none of the IO control policy supports hierarhical groups. But
>> - cgroup interface does allow creation of hierarhical cgroups and internally
>> - IO policies treat them as flat hierarchy.
>> +- Cgroup interface allows creation of hierarchical cgroups. Currently,
>> + internally IO policies are able to treat them as flat hierarchy or
>> + hierarchical hierarchy.
>
> Gui, now we have 2 IO policies. Throttling policy still supports only flat
> mode. Can you please make it clear here that CFQ will support both flat
> and hierarhical mode while throttling supports only flat mode as of today.
>
>> Both hierarchical bandwidth division and flat
>> + bandwidth division are supported. "blkio.use_hierarchy" can be used to
>> + switch between flat mode and hierarchical mode.
>>
>> - So this patch will allow creation of cgroup hierarhcy but at the backend
>> - everything will be treated as flat. So if somebody created a hierarchy like
>> - as follows.
>> + Consider the following CGroup hierarchy:
>>
>> - root
>> - / \
>> - test1 test2
>> - |
>> - test3
>> + Root
>> + / | \
>> + Grp1 Grp2 tsk1
>> + / \
>> + Grp3 tsk2
>>
>> - CFQ and throttling will practically treat all groups at same level.
>> + If blkio.use_hierarchy is disabled in all CGroups, CFQ will practically treat all groups
>> + at the same level.
>>
>> - pivot
>> - / | \ \
>> - root test1 test2 test3
>> + Pivot tree
>> + / | | \
>> + Root Grp1 Grp2 Grp3
>> + / |
>> + tsk1 tsk2
>>
>> - Down the line we can implement hierarchical accounting/control support
>> - and also introduce a new cgroup file "use_hierarchy" which will control
>> - whether cgroup hierarchy is viewed as flat or hierarchical by the policy..
>> - This is how memory controller also has implemented the things.
>> + If blkio.use_hierarchy is enabled in Grp1 and Grp3, CFQ will treat groups and tasks as the
>
> I would think that before this example, we can give one simpler example
> where use_hierarhcy=1 in root cgroup and that would/should lead to all
> children group under root having use_hierarchy=1 set automatically and
> will look as follows.
>
> Pivot tree
> |
> root
> / | |
> tsk1 G1 G2
> / \
> grp3 tsk2
>
> After this now you can give more complicated example as below where
> use_hierarchy=1 is only set for sub branch of tree and not the whole
> tree.

Sure.

>
>> + same view in CGroup hierarchy, it looks as follows.
>> +
>> +
>> + Pivot tree
>> + / | \
>> + Root Grp1 Grp2
>> + / / \
>> + tsk1 Grp3 tsk2
>> +
>> + Root, Grp1 and Grp2 are treated at the same level under Pivot tree. tsk1 stays under Root.
>> + Grp3 and tsk2 are treated at the same level under Grp1. Below is the mapping between
>> + task io priority and io weight:
>> +
>> + prio 0 1 2 3 4 5 6 7
>> + weight 1000 868 740 612 484 356 228 100
>> +
>> + Note1: Regardless of the use_hierarchy setting in Root group, Root group is always put onto
>> + Pivot tree.
>> +
>> + Note2: Currently, "blkio.use_hierarchy" only effects proportional bandwidth division. For
>> + Throttling logic, it still continue to treat everything as flat.
>>
>
> Ok, I see you mentioned throttling flat mode here. I guess it is better
> to clarify it in the beginning itself.

Ok

Thanks,
Gui

>
>> Various user visible config options
>> ===================================
>> @@ -169,6 +190,17 @@ Proportional weight policy files
>> dev weight
>> 8:16 300
>>
>> +- blkio.use_hierarchy
>> + - Switch between hierarchical mode and flat mode as stated above.
>> + blkio.use_hierarchy == 1 means hierarchical mode is enabled.
>> + blkio.use_hierarchy == 0 means flat mode is enabled.
>> + You can set this interface only if there isn't any child CGroup under
>> + this CGroup. If one CGroup's blkio.use_hierarchy is set, the created
>> + children will inherit it. it's not allowed to unset it in children.
>> + The default mode in Root CGroup is flat.
>> + blkio.use_hierarchy only works for proportional bandwidth division
>> + as of today and doesn't have any effect on throttling logic.
>> +
>
> This is good. Makes use_hierarchy behavior for children and subtree very
> clear.
>
>> - blkio.time
>> - disk time allocated to cgroup per device in milliseconds. First
>> two fields specify the major and minor number of the device and
>> --
>> 1.6.5.2
>>
>>
>>
>>
>>
>>
>


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